1. Field of Invention
This invention relates generally to an improvement in diagnostic medical ultrasound imaging, and more specifically to more effective medical imaging of a human or animal due to improved utilization of an ultrasound contrast agent.
2. Description of the Prior Art
Traditionally, ultrasound contrast agents have been imaged by using fundamental imaging or second harmonic imaging. Harmonic imaging is usually preferred over fundamental imaging, because the signal from contrast agents is much larger than that from surrounding tissue. Furthermore, harmonic imaging provides excellent contrast between blood and tissue, and is able to reduce artifacts due to phase aberrations in the body. However, since harmonic imaging still receives signal from tissue, the specificity between contrast agent and tissue is still limited.
Recently, subharmonic imaging has been recognized to be a promising new technique to image contrast agents. However, the biggest advantage of subharmonic imaging is also its biggest drawback. Since tissue does not generate subharmonic signals, clinicians cannot view the underlying anatomy.
Therefore, it would be desirable to combine the advantages of subharmonic imaging with harmonic imaging to image contrast agent and visualize background tissue.